Tellurium imaging composition including improved reductant precursor and method

ABSTRACT

Imaging films and film-forming compositions are provided which include a reducible tellurium compound, a reductant precursor, a source of labile hydrogen incorporated in a matrix. The reductant precursors are of the formulae  &lt;IMAGE&gt;  &lt;IMAGE&gt;  &lt;IMAGE&gt;  where Y1 is alkoxy, Y2 is chloro or alkoxy and Y3 is hydrogen, chloro or alkoxy. Methods are provided for synthesizing the reductant precursors.

THE PRIOR ART BACKGROUND

Various methods are known for producing images or duplicates of images.The imaging materials used are, in certain cases, particular organiccompounds. Some of these heretofore known methods employ mixtures ofinorganic compounds such as silver halide with one or more particulartypes of organic compounds as sensitizers.

A new photographic process using tellurium compounds to provide theimage is disclosed in U.S. patent application Ser. No. 596,646 filedJuly 17, 1975 (now U.S. Pat. No. 4,142,896). In accordance with U.S.Pat. No. 4,142,896, an emulsion is formed using certain reducibletellurium compounds in combination with a reductant precursor in abinder or matrix suitable for forming a film-like coating on asubstrate. The film prepared therefrom is exposed image-wise toactivating energy and is thereafter developed as is known in the arthereinafter described. Heat development is preferred.

Some tellurium compounds described for use in the photographic processof U.S. Pat. No. 4,142,896 may be represented, for example, by theformula

    R.sub.x --Te--X.sub.y                                      ( 1)

in which R is an organic radical containing at least one carbonyl group,X is halogen, preferably chlorine, and x is 1, 2 or 3, and x+y=4. Theorganic radical R may be either two independent radicals or may bejoined together to form a cyclic compound. Another group of compoundsmentioned in U.S. Pat. No. 4,142,896 are organic tellurium compoundswhich may be considered or characterized as tellurium tetrahalideadducts of ethylenic or acetylenic hydrocarbons. Some of such compoundscan be represented by the formulae ##STR2## wherein R and R¹ are eachthe residue of an ethylenic hydrocarbon and X is a halogen, preferablychlorine.

Another category of photosensitive tellurium compounds which have beenfound useful are halogenated tellurium compounds, such as compounds ofthe formula

    TeCl.sub.n Br.sub.m                                        ( 4)

where n is an integer from 2 to 4, and n+m=4. The use of suchhalogenated tellurium compounds in imaging processes is disclosed inU.S. Pat. No. 4,066,460 to Chang et al.

Still another category of useful tellurium compounds are described inU.S. Pat. No. 4,106,939. These compounds are tellurium tetrahalideadducts of aromatic amines in which nitrogen attached directly orindirectly to the aromatic ring is substituted by alkyls of 1-4 carbonatoms, the adduct being free of diazo groups.

The tellurium compounds such as the foregoing may be employed inconjunction with a reductant-precursor which serves as a sensitizer. Thereductant-precursor is a compound which, under the influence ofactivating energy, will absorb radiation energy and abstract labilehydrogen from an appropriate hydrogen donor to become a strong reducingagent. The strong reducing agent reduces the tellurium compound to adivalent tellurium compound or to elemental tellurium. In either event,a change in optical density occurs which results in an imaging suitablefor recording information. In general terms, the foregoing reaction maybe represented by the following mechanism: ##STR3## wherein PQ is thereductant precursor sensitizing agent; ¹ PQ is the first excited singletstate thereof; ₃ PQ is the triplet state thereof; RH is the hydrogendonor; PQ.H₂ is the reductant precursor in its reduced state; and(R¹)₂.Te.X₂ is the reducible tellurium image-forming compound.

In this connection, it should be noted that the hydrogen donor need notbe specifically provided, although a variety of alcohols can be used ifdesired. In the absence of a specially-provided hydrogen donor, thelabile hydrogen can sometimes be abstracted from the organic resins usedas binders. In other cases, the sensitizer can be its own hydrogendonor, and this is known to be the case with at least one sensitizer,namely, isopropoxynaphthoquinone.

A modification of the tellurium photographic process is described inBelgian Patent No. 854,193, wherein certain diols of the formula

    R.sub.10 --CHOH--Z--CHOH--R.sub.11                         ( 5)

may be employed as the hydrogen donor for use in conjunction with thephotosensitizer described above. In the foregoing formula, R₁₀ and R₁₁represent hydrogen and various organic substituents. Z may be a directcarbon-carbon linkage between the two hydroxy substituted carbon atoms,or may be any of various linking groups. Reference is made to BelgianPatent No. 854,193 for a fuller description of the diols referred to. Inthe Belgian patent, these diols are said to serve as hydrogen donors.Subsequent research has suggested that this is not completely accurate.In fact, a major portion of the diol appears to form a complex with thetellurium compound.

This finding has led to the discovery of diols of the general formula

    R--O--CH.sub.2 CHOH--CH.sub.2 OH                           (6)

which have improved characteristics when used in tellurium-basedphotographic films.

The radical R may be a simple aliphatic group (for example, alkyl oralkenyl). Alternatively, the radical R may contain a carbonyl group (forexample, an acyl radical). Preferably, however, the radical R isaromatic. Best results are obtained where the aromatic ring is separatedfrom the ether oxygen by one methylene grouping. A more completedescription of these diols is contained in U.S. patent application Ser.No. 73,700, filed Sept. 10, 1979, now U.S. Pat. No. 4,281,058, andreferences made thereto for additional descriptions thereof.

Still another modification in the use of tellurium compounds asphotosensitive agents involves what is known as a "masked reducingagent". A number of compounds are known, such as phenidone, which willreduce organo-tellurium compounds. The reducing capacity of suchcompounds may be "masked"--i.e., inhibited--by appropriate substitution.In such cases, if the substituent is one which can be cleaved by thereaction products liberated upon the photoreduction of the telluriumcompound, the masked reducing agent can be used to amplify thephotoresponse through the mechanism ##STR4##

Since the organo-tellurium compounds commonly used release hydrogenhalides (particularly hydrogen chlorides) as by-products of thereduction reaction, and the reducing agents, such as phenidone, areamino compounds, the masking agents most effectively employed arecompounds which will convert the amino nitrogen into an amide. A typicalmasked reducing agent thus is the compound ##STR5## A more completedescription of masked reducing agents may be found in Belgian Pat. No.863,052 of July 19, 1978, and reference thereto is made for additionaldescriptions thereof.

As an alternative to the masked reducing agents described in BelgianPat. No. 863,052, a new class of masked reducing agents may besubstituted, represented by the general formulae ##STR6## wherein Y ishydrogen or ##STR7## said compound containing at least one ##STR8##group. In the foregoing formulae, R¹ may be alkyl, alkanoyl,alkoxycarbonyl, phenyl, benzyl, benzoyl, nitrophenyl, benzylcarbonyl,phenylmethyl, phenylethyl or phenylpropylcarbonyl, or aminocarbonyl. R²,R³ and R⁴ each, and independently, may be hydrogen, alkyl or phenyl andamino. R⁴ may be phenyl, nitrophenyl, halophenyl, alkyl, mono-, di- ortri-haloalkyl, benzoyl, alkylphenyl, or alkylcyanophenyl. The maskinggroup may be substituted at either one or both of the amino hydrogensites of the reducing agent. The alkyl groups referred to above maycontain up to seven carbon atoms. Such compounds are convenientlyaccessible through reaction of the parent hydrazine or pyrazoline withan isocyanate of the formula

    R.sup.5 --N═C═O                                    (11)

A more complete description of these masked reducing agents is found inU.S. patent application Ser. No. 277,720, filed June 26, 1981 andreference thereto is made for additional descriptions thereof.

In practice, the foregoing ingredients, i.e., a tellurium derivative, areductant precursor sensitizer, and additional ingredients such as theglycol and masked reducing agent, are combined in a suitable matrix toform an emulsion which may be spread into a film on an appropriatecarrier or substrate. A latent image in the film is formed by exposureto imaging energy, for example, a light image.

After formation of the latent image, a visible image is developed byheating the exposed film as described in U.S. Pat. No. 4,142,896.

The speed or light sensitivity of the film is determined by the amountof energy necessary to produce an image. For many applications it isdesirable to have an imaging film that is relatively fast, and inaddition, has a low optical density relative to the optical density ofthe image formed by the film. It is also desirable for the film to besensitive to light in the visible spectrum facilitating use of the filmin many practical applications. The organo-tellurium imaging systempreviously described generally did not possess the characteristics ofsensitivity to visible light while at the same time having good speed,such as less than about 30,000 ergs of imaging energy per squarecentimeter to achieve an optical density of one greater than fog.

SUMMARY OF THE INVENTION

The present invention concerns an improvement in the above describedorgano-tellurium system for photosensitive emulsions. In accordance withthe invention, organo-tellurium imaging systems are provided which haveexcellent speed (generally less than about 30,000 ergs/cm² to achieve anoptical density of one over fog) and which have excellent sensitivity toelectromagnetic energy in the visible region (400-600 nanometers).

The improved spectral sensitivity is attained by the use of certaintypes of reductant precursors which are quinones. The quinones of thepresent invention may be represented by the general formulae: ##STR9##wherein Y₁ is alkoxy, generally having less than 6 carbon atoms,(methoxy, ethoxy, propoxy, butoxy, pentoxy, etc.), Y₂ is alkoxy,generally having less than 6 carbon atoms (methoxy, ethoxy, propoxy,butoxy, pentoxy, etc.) or chloro and Y₃ is hydrogen, chloro or alkoxy,generally having less than 6 carbon atoms (methoxy, ethoxy, propoxy,butoxy, pentoxy, etc.). Generally, best results are obtained when Y₁ hasgreater than one carbon atom. Use of the quinone compounds in accordancewith the invention results in unexpected improvements in spectralsensitivity and/or speed. The film-forming compositions and films inaccordance with the invention may include one or more of the foregoingquinones.

Representative quinone compounds within the scope of the invention are:3-chloro-2-isopropoxy-1,4-naphthoquinone;3-chloro-2-isopropoxy-1,4-anthraquinone;3-chloro-2-isopropoxy-6,7-diphenyl-1,4-naphthoquinone;3-chloro-2-(3'-pentoxy)-1,4-naphthoquinone;3-chloro-2-(2'-butoxy)-1,4-naphthoquinone;3-chloro-2-(3',3'-dimethyl-2'-butoxy)-1,4-naphthoquinone;2,3-diisopropoxy-1,4-naphthoquinone;3-chloro-2-methoxy-1,4-naphthoquinone; 2,3-dimethoxy-1,4-naphthoquinone;3-chloro-2-(t-butoxy)-1,4-naphthoquinone;3-chloro-2-ethoxy-1,4-naphthoquinone;3-chloro-2-(n-butoxy)1,4-naphthoquinone;3-chloro-2-(2'-methylpropoxy)-1,4-naphthoquinone; and2-isopropoxy-1,4-anthraquinone.

The reductant precursors, when incorporated into the organo-telluriumimaging system results in imaging film having increased sensitivity tovisible light at relatively high speed.

In accordance with another aspect of the present invention, the improvedreductant precursors may be incorporated into imaging systems whichutilize reducible organo-metallic compounds other than telluriumcompounds. For example, copper, cobalt, silver, nickel and mercury aremetals which may form suitable reducible compounds for imaging. However,the same speed and spectral sensitivity may not result as when used inorgano-tellurium imaging systems.

DETAILED DESCRIPTION OF EMULSIONS ACCORDING TO THE PRESENT INVENTION

An emulsion formulated in accordance with the present invention containsa tellurium compound, a reductant precursor of the above description,and an appropriate matrix or binder. Optionally, other components mayalso be included in the emulsion. A masked reducing agent may beincluded, as disclosed in U.S. patent application Ser. No. 277,720 filedJune 26, 1981. A diol may be included, preferably a glyceryl compound ofU.S. Pat. No. 4,281,058. An alcohol may also be included, preferablywhen a glyceryl compound of U.S. Pat. No. 4,281,058 is included, asdisclosed in copending U.S. patent application Ser. No. 392,580 filedJune 28, 1982. Water may also be included, as disclosed in copendingU.S. patent application Ser. No. 392,756 filed June 28, 1982. A base maybe included as disclosed in copending U.S. patent application Ser. No.392,579 filed June 28, 1982.

It is anticipated that reducible organo-metallic imaging compounds andother reducible metal compounds, other than tellurium compounds, may beutilized in accordance with the invention. For example, other metalswhich can form organo-metallic imaging compounds, include copper,silver, nickel, mercury and cobalt. For example, cobalt imagingcompounds are disclosed in U.S. Pat. No. 4,201,588 to Adin et al.Specific organo metallic compounds which may be used include, forexample, copper-2,4-pentanedionate, nickel-2, 4-pentanedionate, mercuryacetate and silver behenate.

The image-forming tellurium: A number of image-forming telluriumcompounds are described in the prior art and such compounds aregenerally useful in the present invention. In general, the presentinvention contemplates using these and other tellurium compounds whichundergo analogous reduction reactions in the presence of a reductantprecursor as hereinafter described.

It has been found that many tellurium compounds possess certainproperties which adapt them especially for use in imaging processes. Ingeneral, these are compounds from which, as a result of the imaging anddeveloping steps generally referred to above, elemental tellurium isdeposited from the tellurium compounds. Tellurium is chain-forming incharacter, and it is generally deposited from the tellurium compoundsuseful for photographic purposes (preferably including thin needles),the compounds being capable of rapid nucleation and growth ascrystallites, which crystallites grow as chains and largely or mainly asneedles. Such chains or needles are opaque and are characterized byexcellent light scattering properties to produce good optical densityobserved after thermal or other development.

Effects which may involve oxide formation are substantially restrictedto surface effects as distinguished from effects which cause degradationthrough the bodies of the needles or chains.

Preferably, the tellurium imaging compound is an organo-telluriumcompound such as disclosed in U.S. Pat. No. 4,142,896 of Chang et al.These compounds are organic tellurium compounds which inherently possesssensitizer properties (and/or may be mixed with a separate sensitizer)in which the tellurium is linked directly to at least one carbon atom orthe organic radical of the organo-tellurium material, the organictellurium compound being of one structure and having a detectablecharacteristic which is capable of undergoing a change in response tothe application of imaging energy in the form of particle or waveradiation to produce a material of different structure having anotherdetectable characteristic. The material having a different structure anddifferent detectable characteristics resulting from the imaging step issometimes referred to as the "image-forming compound".

The tellurium imaging compound may be an organo-metallic compound suchas disclosed in U.S. Pat. No. 4,062,685, which is hereby incorporated byreference.

A particularly advantageous subgroup of the imaging organo-telluriumcompounds utilized in the practice of the present invention comprisesorganic compounds which contain an organo radical and halogen attacheddirectly to the tellurium atom, there being at least one carbonyl groupin the organo radical. Certain of them are adducts of tellurium halides,notably tellurium tetrachloride, with organic compounds, notably ketonesor similar chromophores, containing at least one carbonyl group in theorganic compound. They may, thus, be considered or characterized asorgano-tellurium compounds or adducts containing halogen, namely,chlorine, bromine, iodine, and fluorine, attached directly to thetellurium atom. Most of this particular class or group of said imagingcompounds have two carbonyl-containing organo radicals. Those which areespecially useful in the practice of the present invention have chlorineas the halogen but, in certain cases, although generally lesssatisfactory, other halogens can be present. The imaging compoundsshould be selected to be soluble or homogeneously dispersible in anyparticular matrix material which may be utilized, as is describedhereafter. Many of this group of imaging organo-tellurium compounds maybe represented by the formula

    R.sub.x 13 Te--Hal.sub.y                                   ( 15)

where R is an organo radical containing at least one carbonyl group, Halis halogen, especially chlorine, x is 1, 2 or 3, and x+y=4, subject tothe proviso that Te is linked directly to carbon in an organo radical.Preferably, x is 2 or 3.

Others can be represented by the formula

    R.sub.2 --Te--Hal.sub.4                                    ( 16)

where R is a carbonyl-containing organic radical, and Hal is halogen.

The R radical can be aliphatic, cycloaliphatic or aromatic (mononuclearor dinuclear) or a combination thereof and may contain one or morehetero atoms in the chain or rings. It may be unsubstituted orsubstituted by various organic or inorganic radicals, which may assistin or at least do not interfere with the desired imaging effect,illustrative of such radicals being C₁ -C₆ alkyl, corresponding oxyalkylradicals, acetyl, nitro, C.tbd.N, Cl, Br, F, etc. Generally speaking,the aforesaid organo-tellurium imaging compounds which contain atrihalide group as, for instance, acetophenone tellurium trichloride,tend to have relatively low melting points (about 70°-80° C.), and aremore hygroscopic and less stable than those generally similar compoundscontaining two halogen atoms and, therefore, such trihalides are lessdesirable for use in the practice of the present invention.

A more limited class of this particular subgroup of imagingorgano-tellurium compounds may be represented by the formula

    (Ar--CO--CH.sub.2).sub.2 Te--Hal.sub.2                     ( 17)

where Ar is an aromatic hydrocarbon radical, which may be substituted orunsubstituted, as indicated above, and Hal is halogen, especiallychlorine. This subgroup of compounds, particularly where Hal ischlorine, represents especially advantageous embodiments of theinvention, with respect to the imaging organo-tellurium compounds whichare used in the practice of the present invention.

Another subgroup of imaging organo-tellurium compounds, useful in thepractice of and contemplated by the present invention, which do notcontain a carbonyl group in an organo radical but in which tellurium islinked directly to carbon are compounds which may be considered orcharacterized as tellurium tetrahalide adducts of ethylenic or ofacetylenic hydrocarbons. These compounds are generally convenientlyproduced by reacting 1 to 2 moles, particularly 2 moles, of theethylenic or acetyleneic hydrocarbon with 1 mole of telluriumtetrahalide, especially preferred for such use being TeCl₄. Certain ofsuch compounds can be represented by the formulae: ##STR10## where R³and R² are each the residue of an ethylenic hydrocarbon, for instance,an alkene or a cycloalkene, Hal is chlorine, bromine or iodine,especially chlorine, x is 1 to 3, and x+y=4.

Illustrative of the ethylenic and acetyleneic hydrocarbons which can beadducted with tellurium tetrahalides to produce such imagingorgano-tellurium compounds are propylene; butene-1; isobutylene;butene-2; 2,3-dimethyl-2-butene; 3,3-dimethyl-1-butene;2,4-dimethyl-1-pentene; 4,4-dimethyl-1-pentene; 2,5-dimethyl-3-hexene;dipentene; 1,1-diphenylethylene; 1-heptene; 1-hexene; 2-methyl-1-hexene;3-methyl-1-hexene; 4-methyl-1-hexene; 2-ethyl-1-hexene;2-isopropyl-1-hexene; 2-methyl-1-pentene; 2-methyl-2-pentene;2-ethyl-2-pentene; 3-methyl-1-pentene; piperylene; vinylcyclohexene;vinylcyclopentene; 2-vinylnaphthalene; 1,2,4-trivinylcyclohexene;4-methyl-1-cyclohexene; 3-methyl-1-cyclohexene; 1-methyl-1-cyclohexene;1-methyl-1-cyclopentene; cycloheptene; cyclopentene; cyclohexene;4,4-dimethyl-1-cyclohexene; 2-methylbutene-1; 3-methylbutene-1; and1-octene; lower alkyl and lower alkoxy derivatives of various of thealkenes such as cyclohexene; 1-pentyne; 2-pentyne; 1-hexyne; and3-methyl-1-butyne.

The preparation of the aforementioned organic tellurium compounds aswell as many examples thereof are more fully set forth in U.S. Pat. No.4,142,696, which is hereby incorporated by reference.

As indicated above, tetrahalides of tellurium in which the halide is atleast one member selected from the group consisting of chlorine andbromine are also useful as the image-forming material in the presentinvention. Such tellurium halides are fully described in U.S. Pat. No.4,066,460, the specification of which is hereby incorporated byreference. Certain of these imaging materials can be represented by theformula

    TeCl.sub.n Br.sub.m                                        ( 20)

where n is an integer from 1 to 4 and m+n=4. Typical telluriumtetrahalides which may be used are TeCl₄ ; TeCl₂ Br₂ ; and TeClBr₃.TeCl₄ is especially useful. Reference is made to U.S. Pat. No. 4,066,460for a fuller description of these tellurium tetrahalides and their useas imageforming compounds.

Still another group of image-forming compounds are certain compoundsderived from tellurium tetrahalides which are described in U.S. Pat. No.4,106,939 to Chang et al. These involved compounds are adducts oftellurium tetrahalide with aromatic amines exemplified by the telluriumtetrachloride adduct of dimethylaniline, which adduct is free of diazogroups. More specifically, these tellurium tetrahalide adducts areformed by combining a tellurium tetrahalide with an aromatic amine inwhich nitrogen attached directly or indirectly to the aromatic radicalis substituted by alkyls containing from 1 to 4 carbon atoms, theimaging organo-tellurium material being free from diazo groups.

These aromatic amine adducts of the tellurium tetrahalides are fullydescribed in U.S. Pat. No. 4,106,939 to Chang et al.; the disclosurethereof is hereby incorporated by reference.

The active tellurium compounds may, if desired, be formed in situ, forexample, by using a tellurium oxide or a tellurium salt in combinationwith a suitable organic compound. Sometimes the in situ formation ispromoted by the presence of an acid. For example, bis(acetophenone)tellurium dichloride or tellurium oxide or alkali metal tellurates maybe combined with one of the glycols described below to form atellurium-organic compound complex which is active. It is believed thatthe reaction is analogous to the reaction between organic telluriumcompounds such as described above and a diol. Preliminary informationsuggests that the reaction is favored by an acidic medium. Small amountsof an acid such as anhydrous hydrogen chloride may be added.Alternatively, halogen-containing tellurium compounds will provide therequisite acidity.

The reductant precursor: In addition to the tellurium image-formingcompound, the imaging systems of the present invention include areductant precursor, or sensitizer, which, as described above, is acompound that, under the influence of activating energy, has theproperty of extracting labile hydrogen from a hydrogen donor to become areducing agent with respect to the image-forming tellurium compound. Theactivated reducing agent then reduces the tellurium compound to producethe desired image. The hydrogen donor may be an external source ofhydrogen such as an alcohol specifically provided for the purpose.However, the hydrogen donor may equally well be an appropriate groupwhich is a part of the molecular structure of the reductant precursor.

Preferred reductant precursors include:3-chloro-2-isopropoxy-1,4-naphthoquinone;3-chloro-2-isopropoxy-1,4-anthraquinone;3-chloro-2-isopropoxy-6,7-diphenyl-1,4-naphthoquinone;3-chloro-2-(3'-pentoxy)-1,4-naphthoquinone;3-chloro-2-(2'-butoxy)-1,4-naphthoquinone; 3-chloro-2-(3',3'-dimethyl-2'-butoxy)-1,4-naphthoquinone;2,3-diisopropoxy-1,4-naphthoquinone;3-chloro-2-methoxy-1,4-naphthoquinone; 2,3-dimethoxy-1,4-naphthoquinone;3-chloro-2-(t-butoxy)-1,4-naphthoquinone;3-chloro-2-ethoxy-1,4-naphthoquinone;3-chloro-2-(n-butoxy)1,4-naphthoquinone;3-chloro-2-(2'-methylpropoxy)-1,4-naphthoquinone; and2-isopropoxy-1,4-anthraquinone.

It will be understood that not all reductant precursors will beeffective or equally effective, with each given imaging material, eventaking into account the utilization of imaging energy in the sensitivityrange of the reductant precursor employed and that suitable selectionsof combinations of particular imaging materials and particular reductantprecursors will be required to be made for achieving desirable oroptimum results. Such selections, however, can be made relativelyreadily.

In general, in connection with the foregoing matters, it may be notedthat reductant precursors have ηπ* states, both singlet and triplet, oflower energies than π, π* states and, at least in most cases, compoundswhich have their π, π* states of lowest energy will not bephotosensitively effective, although, in certain limited cases,compounds which fulfill the test of having lower energy η→π* than π→π*transitions do not function as reductant precursors. However, the aboveconsideration is, in the main, an effective one for determining inadvance whether a given compound will function as a reductant precursorfor use in the practice of the present invention. In any event, a simplepreliminary empirical test in any given instance can readily be carriedout if necessary by preparing a test emulsion using the desired imagingcompound and reductant precursor.

Preparation of the Reductant Precursors: Preparation of the reductantprecursors in accordance with the invention is now described. Generally,to form the naphthoquinones or anthraquinones in accordance with theinvention, a suitable starting material is reacted with a suitablealkoxide to form the desired reductant precursor.

When it is desired to form a reductant precursor of the general formula##STR11## wherein Y₁ is alkoxy and Y₂ is alkoxy or Chloro,2,3-dichloro-1,4-naphthoquinone is reacted with a metal alkoxide, suchas a sodium alkoxide, the alkoxide corresponding with the desired alkoxygroup. The metal alkoxide can be formed by reacting an alcohol with anactive metal, such as sodium. For example, the reaction of sodium withisopropanol yields sodium isopropoxide. Thus, to prepare2,3-diisopropoxy-1,4-naphthoquinone, sodium isopropoxide is reacted with2,3-dichloro-1,4-naphthoquinone, preferably at room temperature, forming2,3-diisopropoxy-1,4-naphthoquinone.2-chloro-3-isopropoxy-1,4-naphthoquinone is prepared in a similarmanner, except that the alkoxide is added slowly to a cooled (preferably0°-5° C. or about ice bath temperature) suspension of2,3-dichloro-1,4-naphthoquinone. In this manner, only one of the chlorogroups is replaced by an isopropoxy group. Other reductant precursors inaccordance with the invention having one alkoxy group and one chlorogroup, such as 3-chloro-2-(2'-butoxy)-1,4-naphthoquinone,2-chloro-3-isopropoxy-1,4-anthraquinone and2-chloro-3-isopropoxy-6,7-diphenyl-1,4-naphthoquinone, can be preparedin a similar manner. The latter two compounds would be prepared from2,3-dichloro-1,4-anthraquinone and2,3-dichloro-6,7-diphenyl-1,4-naphthoquinone, respectively.

If Y₁ and Y₂ are different alkoxy, one alkoxide is added slowly toreplace one chloro and the product recovered and then the product isreacted in a similar manner with the other alkoxide.

Reductant precursors of the general formula ##STR12## where Y₁ is alkoxyand Y₃ is hydrogen, chloro or alkoxy can be prepared by reacting2-chloro-1,4-anthraquinone (if Y₃ is to be hydrogen) or2,3-dichloro-1,4-anthraquinone (if Y₃ is to be chloro or alkoxy) with asuitable metal alkoxide as previously described with respect to thenaphthoquinones.

Reductant precursors of the general formula ##STR13## where Y₁ is alkoxyand Y₃ is hydrogen, chloro or alkoxy can be prepared by reacting2,3-diphenylbutadiene with 2,3-dichlorobenzoquinone in acetic acid togive 2,3-dichloro-6,7-diphenyl-1,4-naphthoquinone, which is then reactedwith a metal alkoxide as previously described with respect to2,3-dichloro-1,4-naphthoquinone. Alternatively, where Y₄ is hydrogen,2-chlorobenzoquinone is utilized in place of 2,3-dichlorobenzoquinone.

The Masked Reducing Agent: In accordance with the invention, a maskedreducing agent is included. A typical masked reducing agent thus is thecompound 1-phenyl-2-benzoylamido-3-pyrazolidinone ##STR14## A morecomplete description of masked reducing agents may be found in BelgianPat. No. 863,052 of July 19, 1978, and reference thereto is made foradditional descriptions thereof.

As an alternative to the masked reducing agents described in BelgianPat. No. 863,052, a new class of masked reducing agents may besubstituted, represented by the general formulae

    R.sup.1 --NY--NY.sub.2 ; ##STR15## wherein Y is hydrogen or ##STR16## said compound containing at least one ##STR17## group. In the foregoing formulae R.sup.1 may be alkyl, alkanoyl, alkoxycarbonyl, phenyl, benzyl, benzoyl, nitrophenyl, benzylcarbonyl, phenylmethyl, phenylethyl or phenylpropylcarbonyl, or aminocarbonyl. R.sup.2, R.sup.b 3 and R.sup.4 each, and independently, may be hydrogen, alkyl or phenyl and amino. R.sup.4 may be phenyl, nitrophenyl, halophenyl, alkyl, mono-, di- or tri-haloalkyl, benzoyl, alkylphenyl, or alkylcyanophenyl. The masking group may be substituted at either one or both of the amino hydrogen sites of the reducing agent. The alkyl groups referred to above may contain up to seven carbon atoms. Such compounds are conveniently accessible through reaction of the parent hydrazine or pyrazoline with an isocyanate of the formula

    R.sup.5 --N═C═O

A more complete description of these masked reducing agents is found inU.S. patent application Ser. No. 277,720, filed June 26, 1981 which ishereby incorporated by reference

The Base: When a masked reducing agent is utilized, a base can beincluded. The inclusion of a base provides the unexpected result ofimproving the speed (light sensitivity) and/or improving the opticaldensity of the exposed portions after development of imaging film madewith such compositions. The inclusion of a base may also reduce thebackground fog or optical density of unexposed portions of the film.

The base may be organic or inorganic and should be sufficiently alkalineto ionize the masked reducing agent. In general, any base which improvesthe performance of the film, such as, for example, increased speed,increased optical density of exposed portions or decreased fog ofunexposed portions, can be utilized. Preferably, bases which produceunwanted deleterious effects will be avoided. Suitable inorganic basesinclude, for example, metal hydroxides and ammonium hydroxide. Morespecifically, alkali metalhydroxides and alkaline earth metal hydroxidescan be utilized. Useful alkali metal hydroxides include those oflithium, sodium, potassium, rubidium, and cesium. Lithium hydroxide isthe preferred alkali metal hydroxide. Useful alkaline earth metalhydroxides include those of magnesium, calcium and barium. The hydratedform of the metal hydroxide can be used. It is anticipated that morethan one base can be included in the imaging film composition.

Alternatively, the organic base may be an amine compound or a nitrogenatom containing heterocyclic compound.

Suitable amines for use in accordance with the invention includeprimary, secondary and tertiary amines which may be aliphatic oraromatic. More particularly, suitable amines are those such as, forexample, methylamine, dimethylamine, trimethylamine, ethylamine,diethylamine, triethylamine, n-, di-n- and tri-n- propylamine,isopropylamine, n-butylamine, isobutylamine, di-n-butylamine,tertbutylamine, and n-tetradecylamine. In general, those amines of thefollowing formula may be suitable:

    R--NH.sub.2

where R is aliphatic (for example CH₃, C₂ H₅, C₃ H₇, etc.).

The R radical may be unsubstituted or substituted by various organic orinorganic radicals, which do not interfere with the desired imagingeffect.

Cyclic compounds, such as pyridine and piperidine, are also suitable,and may be unsubstituted or substituted by various organic or inorganicradicals, which do not interfere with the desired imaging effect.

While not wishing to be bound by theory, it is believed that the baseionizes the masked reducing agent facilitating the formation of acomplex between the ionized masked reducing agent, positive telluriumions and the latent image formed by the reductant precursor afterexposure of the film to imaging energy. The complex is believed to bevery susceptible to electron transfer, facilitating formation of avisible image.

In general, alkaline earth or alkali metal hydroxides are preferred overorganic bases. The metal ions from the base may form a beneficialcomplex with the reductant precursor which makes the reductant precursormore active.

The amount of base present in the film-forming composition is variable.Generally, there is no minimum amount of base required to provide animproved film. However, the degree of improvement is related to theamount of base present, up to a certain amount, for each particular filmformulation and base. Beyond that amount, generally the photoresponse ofthe film diminishes. The optimum amount of a particular base for aparticular formulation can easily be determined simply by formulatingfilm-forming compositions containing various amounts of a particularbase and testing the performance of the films made therefrom.

The Diol: In accordance with the present invention, there may also beincluded a diol which reacts with the tellurium compound to form anactive intermediate complex. While the chemistry of the complex is notwell understood, we believe that, in general, the complex requiresapproximately 2 moles of diol for each mole of tellurium. Preferably,the diol, when present, is used in excess of the minimum amount to forma complex since the diol will also function as a source of labilehydrogen to provide the source of hydrogen required in the reaction ofthe reductant precursor.

While the present invention involving the use of certain reductantprecursors can be practiced without the inclusion of a diol, thepresence of a diol is preferred especially when a masked reducing agentis present. The presence of a diol serves to markedly reduce the opticaldensity of unexposed areas (i.e., thus increasing the contrast betweenthe exposed and unexposed areas) particularly when a masked reducingagent is present. Thus, while masked reducing agents can be used in theabsence of a diol, tellurium film compositions containing maskedreducing agents tend to have a relatively high optical density in theunexposed areas because the reducing capacity of the masked reducingagent is not fully inhibited by the masking group.

One group of diols which may be used in formulating imaging compositionsare diols of the formula ##STR18## wherein each of R⁴ and R⁵independently represents hydrogen, a hydrocarbon group, includingstraight chain, branched chain and cyclic hydrocarbon groups,hydroxyalkyl groups, alkoxycarbonyl groups, cycloalkyl groups or arylgroups; and Z represents an arylene group (for example, phenylene), thegroup (--C.tbd.C--), the group (--CR⁶ ═CR⁷)_(n), wherein n represents awhole number, for example, 1 or 2, and each of R⁶ and R⁷ representshydrogen or an alkyl group or taken from part of a carbocyclic orheterocyclic ring. Z also may be omitted--that is, the twohydroxy-substituted carbons are joined directly to each other. Thefollowing table illustrates a number of diols which may be used:

    ______________________________________                                        No. of                              Boiling Point                             the                                 (BP) °C. or                        Com-                                Melting Point                             pound R.sup.4    Z         R.sup.5  (MP) °C.                           ______________________________________                                        1     H          --        H        BP   198                                         ##STR19## --        H        MP   67                                     3   H.sub.3 C  --        H        BP   189                                  4     H.sub.3 C  --        CH.sub.3 BP   183                                  5     H          CC        H        MP   52-54                                  6   H                                                                                         ##STR20##                                                                              H        MP   112                                    7   HO(CH.sub.2).sub.4                                                                       --        H        BP   178/5                                                                         mm Hg                                  8                                                                                  ##STR21## --                                                                                       ##STR22##                                                                             BP   280                                  ______________________________________                                    

A fuller description of the foregoing diols may be found in Belgian Pat.No. 854,193, the disclosure of which is hereby incorporated byreference. Preferably, however, the diol is of a more complex type thandisclosed in the above-mentiond Belgian patent application. These morecomplex diols are the subject matter of U.S. Pat. No. 4,281,058, whichis hereby incorporated by reference.

The preferred diols, as described in U.S. Pat. No. 4,281,058, arecompounds of the formula

    R.sup.8 --O--CH.sub.2 --CHOH--CH.sub.2 OH In the foregoing compound, R.sup.8 may be alkyl, acyl, thiazolinyl, alkenyl, phenyl, alkylphenyl, alkenylphenyl, hydroxyalkylphenyl, benzyl, alkylbenzyl, alkoxybenzyl, hydroxyalkylbenzyl, and halobenzyl and similar radicals.

The "thio" analogs of the foregoing compounds can be used (i.e.,compounds in which the radical R⁸ is joined to the glycerol residue by athio linkage in place of the oxy linkage.

Preferred compounds of the foregoing structure are those in which theradical R⁸ is benzyl or a substituted benzyl. The use of the diols ofthe foregoing structure has been found to be preferred since they aremore effective in reducing the optical density of the unexposed areasthan are the diols described in Belgian Pat. No. 854,193.

Ancillary Ingredients: In addition to the foregoing principalingredients of the present formulation, ancillary ingredients may beincluded for various purposes. Thus, for example, it has been found thatcertain materials enhance the shelf life of unexposed virgin dry filmcompositions of the present invention, and in certain instances, theyalso enhance the sensitivity of said film compositions. Illustrativeembodiments of such additional or supplemental materials, which containether or polyether linkages in the molecules thereof, are such materialsor polymers as polyethylene- 20 sorbitan monolaurate; polyethylene-20sorbitan monooleate; Polyox-10; Polyox-80; Polyox-750; polyethyleneglycol-400 distearate; polyethylene glycol-600 distearate; poly(1,3-dioxolane); poly (tetrahydrofuran); poly (1,3dioxepane); poly(1,3-dioxane); polyacetaldehydes; polyoxymethylenes; fatty acid estersof polyoxymethylenes; poly (cyclohexane methylene oxide); poly(4-methyl-1,3-dioxane); polyoxetanes; polyphenylene oxides; poly[3,3-bis (halomethyl) oxocyclobutane]; poly (oxypropylene) glycol epoxyresins; and copolymers of propylene oxides and styrene oxides. Suchmaterials can be incorporated in the imaging film compositions invarying amounts, generally from 5 to 20% by weight of the solid imagingfilm compositions. In certain cases they enhance or prolong the shelflife or storage life, under given storage conditions, as much as 50% oreven very substantially more timewise, and, as indicated, they also, invarious cases, effectively increase film sensitivity.

Again, the inclusion in the imaging films of reducing sugars has beenfound, generally speaking, to bring about an enhancement in density ofthe image area (O.D. image--O.D. background), when the film is imaged asdisclosed above and then developed, for instance, at about 120°-150° C.and for the order of about 15 seconds, especially where the imaging filmis freshly prepared or not older than about a day after initialpreparation. Such films, when exposed to imaging energy and thendeveloped resulted in the production of a positive image (i.e., theoptical density is greater in the nonexposed areas than in the exposedareas) in contrast to the negative working system which exists in theusual practice of the present invention. The inclusion of reducingsugars in the imaging compositions also enables development of theimage, after exposure to imaging energy, to take place at lowertemperatures, even at room temperatures, in a period of several hours,for instance, commonly in 10, 12 or 15 hours. The reducing sugars whichcan be employed are many, illustrative of which are dextrose, glucose,arabinose, erythrose, fructose, galactose, fucose, mannose and ribose.Especially effective are dextrose, arabinose, galactose, fucose andribose. The reducing sugars can be used in variable amounts, butgenerally in equivalent amounts, or somewhat smaller or greater, inrelation to the amount of imaging organo-tellurium materials in theimaging compositions.

It may be desirable in many cases to include a small amount of siliconeoil or similar material as is well known to aid in coating of smoothcontinuous films.

Several other ancillary ingredients may be utilized, which can have theeffect of increasing the sensitivity of the film and/or optical densityafter exposure. These ancillary ingredients include: indoaniline dyes ofthe general formula ##STR23## where R¹ -R⁴ may be, each andindependently, hydrogen or alkyl(N,N-(p-dimethylaminophenyl)-1,4-naphthoquinone (indophenol blue) forexample); indane-1,3-dione derivatives such as 2-phenylindane-1,3-dione;and cyanine dyes of the general formula ##STR24## where n=1, 2 or 3 andX is chloro or iodo (1,1',-diethyl-2, 2'-carbocyamine chloride(pinacyanol chloride), for example).

The matrix material: A film composition in accordance with the presentinvention is completed by dissolving the ingredients and optionalingredients described above in a suitable matrix. The matrix should beas concentrated as is practicable in the active ingredients, i.e., theleast amount of matrix is preferably used. The amount of matrix shouldbe sufficient as to just retain the various active ingredients in asolid solution. An additional quantity of matrix may be used, however,that obviously tends to dilute the concentration of active ingredients,thereby slowing down the photo-response of the film composition. Theselection of matrix materials, of course, must be related to the activeingredients used so as to provide the maximum solubility for anyparticular composition.

The matrix materials, into which the imaging organotellurium materials,and the separate sensitizers when employed, are incorporated to producethe imaging film or coating, are solids at room temperature, and theycan be selected from a relatively large number of materials. Care shouldbe taken to insure that the matrix material does not absorb undesiredcomponents, such as water from the atmosphere. They should desirably beat least in part of amorphous character and it is especially desirablethat they be glassy, polar amorphous materials having a glass transitiontemperature, which desirably should not exceed about 200° C. and may beas low as about 50° C., and, better still, should be within the range ofabout 80°-120° C. They are generally polymeric materials. Illustrativethereof are cyanoethylated starches, celluloses and amyloses having adegree of substitution of cyanoethylation of ≧2; polyvinyl-benzophenone;polyvinylidene chloride; polyethylene terephthalate ("MYLAR"); celluloseesters and ethers such as cellulose acetate, cellulose propionate,cellulose butyrate, cellulose acetate butyrate, acetyl cellulose, methylcellulose, ethyl cellulose, hydroxypropyl cellulose, polyvinylcarbazole;polyvinyl chloride; polyvinyl methyl ketone; polyvinyl alcohol;polyvinylpyrrolidone; polyvinyl methyl ether; copolymers of vinylidenechloride and acrylonitrile; polyvinyl acetate, polyvinyl butylral;polystyrene; polymethyl methacrylate; polyvinyl pyrrolidone;styrenebutadiene copolymers; polyamides; polyacrylic and polymethacrylicalkyl esters such as polymethyl methacrylate and polyethyl methacrylate;copolymer of polyvinyl methyl ether and maleic anhydride; various gradesof polyvinyl formal resins such as so-called 12/85, 6/95E, 15/95S,15/95E, B-79, B-98, and the like, sold under the trademark "FORMVAR"-(Monsanto Company). Of special utility is polyvinyl formal 15/95% whichis a white, free flowing powder having a molecular weight in the rangeof 24,000-40,000 and a formal content expressed as percent polyvinylformal of approximately 82%, possessing high thermal stability,excellent mechanical durability, and resistance to such materials asaliphatic hydrocarbons, and mineral, animal and vegetable oils. Thesepolymeric materials or resins and their preparation are well known tothe art. Also of special utility are various grades of cellulose acetatebutyrate polymers sold by the Eastman Kodak Company under the tradedesignation "CAB", particularly "CAB 500-5".

In addition to their functioning as carriers for and holding together ina unitary composition the imaging organo-tellurium materials,sensitizers and any other ingredients which may be incorporated into theimaging film or coating or layer and their functioning as dry oressentially dry film-forming materials to provide thin films andproviding mechanical durability in the finished imaged film, at leastmany of them appear also to play a chemical or physical role in theimaging process by providing, importantly, a source of readily easilyabstractable hydrogen and, thus, appear to play a significant role inthe latent image formation mechanism, as discussed hereafter. In certaininstances, it may be desirable to decrease the viscosity of the matrix,which can be done, by way of illustration, by the addition of certainplasticizers, for instance, dibutylphthalate or diphenylphthalate, whichadditions tend to result in the production of images desirably of higheroptical densities but which, however, also tend to have the disadvantageof increasing background fogging.

It may be noted that matrix materials of the type which contain basicgroups may complex with the imaging organotellurium materials and,therefore, to the extent that such complexing may occur, the use of suchmatrix materials should be avoided.

Water: The compositions may also include water. A small quantity ofwater, generally added to the matrix material, prior to combination withthe other film-forming components, serves to improve the speed of thefilm. However, too much water may cause a tellurium oxide to beprecipitated when the components of the film-forming composition arecombined, and this should be avoided. For a more complete description ofthe inclusion of water, reference is made to U.S. patent applicationSer. No. 392,576 filed June 28, 1982.

Alcohol: The compositions of the invention may also include an alcohol.Preferably, the alcohol will be utilized when a diol as previouslydescribed is present in the composition. The alcohol and diol may form acomplex with the tellurium compound, providing a film having enhancedspeed and/or improved background fog. The alcohol may be primary,secondary or tertiary. Primary monohydric alcohols are preferred, suchas n-butanol and n-propanol, for example. For a more completedescription of the inclusion of an alcohol, reference is made to U.S.patent applicaton Ser. No. 392,580 filed June 28, 1982.

Formulation of Film Compositions: In the production of the films or thinlayers of the imaging material compositions, which are generallyprepared in the form of solutions or homogeneous dispersions and coatedor laid down on a substrate, it is especially desirable to dissolve orhomogeneously disperse the ingredients in an organic solvent.Illustrative of suitable solvents are methyl ethyl ketone (MEK),dimethylformamide (DMF), chloroform, tetrahydrofuran (THF),dimethylacetamide (DMA), dioxane, dichloromethane and ethylenedichloride, or compatible mixtures of such organic solvents or withother organic solvents. A particularly useful solvent is a 50:50 mixtureof dichloromethane and methyl ethyl ketone. After the solution orhomogeneous dispersion is filmed on a substrate in any suitable manner,the major proportions of such organic solvent or solvents are evaporatedoff, preferably at a relatively low temperature and, sometimesdesirably, under subatmospheric pressures or in vacuo, until the film orcoating is substantially dry to the touch, such dry-to-the-touch coatingbeing especially desirable for handling and processing purposes.Although such films or coatings may be, generally speaking, dry to thetouch, it should be understood that this does not mean that the film isfree from organic solvent. Indeed, it has been found that it isfrequently very desirable that the finished films or coatings, prior toexposure to imaging energy, contain a small percentage, commonly of thegeneral order of about 2 to 3%, by weight of the film or coating, ororganic solvent, for instance, dimethylformamide (DMF) since itspresence appears to play a favorable role in the sensitivity of thesystem in relation to the latent image formation and/or ultimate imageobtained after the development step. The elimination of all oressentially all of the DMF, or other organic solvent or solvents, fromthe virgin film prior to the imaging and development frequently leads toa decrease in sensitivity. In any event, in any given instance wheredrying of the virgin imaging film has been carried out to a point whereessentially no organic solvent is present, and whereby sensitivity isunduly reduced, sensitivity can be increased or restored by adding asmall amount of organic solvent to the film prior to exposing it toimaging energy.

The imaging film or coating thickness are variable but will usually fallwithin the range of about 1 to about 35 μm with about 5 to 15 μmgenerally being a good average. In thickness in terms of millimeters(mm), such may vary from about 0.0005 to about 0.05 mm, or much greater,such as from 0.05 to 5 mm, the selected thickness being dependent uponthe particular use to which the imaging film is to be put.

The production of the imaging organo-tellurium materials, and thecoating, handling and processing operations, to the extent which may berequired, are carried out under appropriate light conditions, as thoseskilled in the art will readily understand. For instance, theformulation of the coating compositions and the coating and dryingoperations are conveniently carried out under amberlite filtered light(weak transmission at 550 nm). The dry film prior to imaging, isdesirably stored in the dark. In certain cases, avoidance of contact ofcertain of the ingredients with certain metals may be in order whereundesired reactions, such as reductions, may occur. In general, thevessels or containers, stirrers, etc., utilized should be made of glassor other vitreous materials or other materials inert to the coatingingredients to insure against contamination or possible undesiredreactions. It is advantageous, in general, to prepare the imagingcompositions shortly prior to coating them on the selected substrate.Under suitable storage conditions, which generally are conditions ofdarkness and reasonable avoidance of air or oxidizing atmospheres andhumidity conditions, the stability of the imaging compositions is good.

In the imaging compositions, the proportions of the matrix, the imagingorgano-tellurium material and the reductant precursor are variable. Inthose special cases where the imaging organo-tellurium material utilizedis one which also inherently or concomitantly possesses desiredsensitizing properties, as noted above, a separate reductant precursoris not necessary. It may, however, even in such cases, be desirable toemploy a separate or added reductant precursor which may be of entirelydifferent sensitizing properties from that inherently possessed by theparticular imaging organo-tellurium material utilized. In any event,generally speaking, excluding the organic solvent or solvents, whereemployed as described below, at least in most cases the matrix material,which is a normally solid material, that is, solid at room temperature,will be employed in amounts in excess of any one of the other materialsand will also usually be present in major amount, that is more than 50%and broadly in the range up to 90% by weight, of the total materialspresent in the imaging composition. The imaging organo-telluriummaterial, generally also a normally solid material, will ordinarilyconstitute from about 1 to above 20 parts per 100 parts of matrix,usually about 5-10 parts per 100 parts of matrix. The reductantprecursor, which is usually a solid, will usually be employed in lesserproportions, commonly of the order of about 5 to 20%, usually about 6 to15%, by weight, of the imaging composition, although, in certain casesthe proportions thereof can be substantially higher, approximately oreven exceeding somewhat the proportions of the imaging organo-telluriummaterial. With further regard to the proportions of the aforesaidingredients, it may be stated that the area density of the reductantprecursor is desirably selected so that about 70-95% of the photonsfalling on the film in the region of the absorption bands of thereductant precursor are absorbed. Considerably higher concentrations ofreductant precursor would leave the dark side of the film unexposed andno advantage would thus be served. In general, for optimal results inmany cases, the mole concentration of the imaging organo-telluriummaterial should be reasonably close to or roughly approximate to that ofthe reductant precursor. The concentration of the polymer matrixmaterial should be sufficient to produce an essentially amorphous filmwithout bringing about precipitation of the imaging organo-telluriummaterial, the sensitizer and other supplemental ingredients whenutilized. Excess polymer matrix material also tends to decrease thesensitivity of the film.

The amount of diol should be present in a concentration sufficient toprovide at least 2 moles of diol for each mole of tellurium compound,and preferably to provide up to a ratio of 6:1 moles. As indicatedabove, our work has suggested that a complex is formed between the dioland the tellurium compound in a molar ratio of 2:1, and that excess diolabove that is useful to provide a source of labile hydrogen for reactionwith the reductant precursor. Larger amounts of the diol may be used ifdesired. To some extent, improved results are obtained when these largeramounts of diol are used; however, there is a point of diminishingreturns above which increasing the amount of diol will not providecommensurate improvement in photoresponse of the finished film.

The masked reducing agent may be present in amounts of 1% up to 200% byweight of the tellurium compounds. Measurably improved sensitivity canbe found in accordance with the present invention with even very smallamounts of masked reducing agent and within limitations the degree ofimprovement is in proportion to the amount of masked reducing agentwhich is incorporated in the film. Again, however, a law of diminishingreturns is observed, and while large amounts of the masked reducingagent will be incorporated--in the order of 2 to 4 times the amount oftellurium compound--beyond these large amounts the increase inphotoresponse obtained is not commensurate with the increased amount ofmasked reducing agent incorporated.

The film-forming compositions as described above will be applied to anysuitable substrate. Glass, porcelain, paper and various plasticsubstrates have been found suitable. For the purposes of formingfilm-like materials, transparency is obviously desirable. For thispurpose, film of polyethylene terephthalate have been found particularlysuitable. Other substrates include, for example, polyimides, nylon andtriacetyl cellulose.

Fixing: After exposure and development, which development may beaccomplished by heating, the film may be fixed as described in U.S. Pat.No. 4,142,896. The film may also be fixed by contacting the film with analcohol, such as isopropanol, for example. A small amount of ketone suchas acetone, for example, may also be included with the alcohol.Especially useful is a solution of 50 parts isopropanol/1 part acetone(by volume).

Additional considerations which those skilled in the art in formulatingand using tellurium-based film compositions may utilize are apparentfrom U.S. Pat. No. 4,142,896, the disclosure of which is herebyincorporated by reference.

This invention is further illustrated by the following examples:

EXAMPLE 1

A reductant precursor in accordance with the invention,2-chloro-3-isopropoxy-1,4-naphthoquinone (CIPNQ), was prepared ashereinafter described. 3.5 grams of sodium and 100 ml of isopropanolwere refluxed in 200 ml of benzene, to prepare the alkoxide, sodiumisopropoxide. An additional 150 ml of benzene was added after all thesodium dissolved in order to prevent the precipitation of the alkoxide.The diluted alkoxide was then added drop-wise to a previously cooledsuspension of 30 grams of 2,3-dichloro-1,4-naphthoquinone in 200 ml ofbenzene at 0-5° C. The reaction was carried out under red light sincethe product is light sensitive. The reaction was complete within 30minutes. The reaction mixture was then washed with water and crudeproduct was obtained after the organic layer was dried and concentrated.Recrystallization in methanol yielded 25 grams of pure, yellow, shinycrystals of CIPNQ.

EXAMPLE 2

A reductant precursor in accordance with the invention,2,3-diisopropoxy-1,4-naphthoquinone (DIPNQ), was prepared as hereinafterdescribed. The alkoxide was prepared by reflexing 3 grams of sodium and200 ml isopropanol in 200 ml benzene. After all the sodium dissolved,the alkoxide solution was added slowly to a suspension of 10 grams of2,3-dichloro -1,4-naphthoquinone in 50 ml isopropanol at roomtemperature. The reaction mixture was acidified with 4 N HCl andextracted with benzene. The organic layer was dried and concentrated.The crude product thus obtained was purified by dissolving it in 100 mlof benzene and washing with several portions of 2.5% aqueous NaOH untilthe wash solution was colorless. 6 grams of pure dark red DIPNQ liquidwas obtained after the washed benzene layer was dried, decolorized andconcentrated. The decolorizing agent was Norit A®, marketed by the J.T.Baker Chemical Company.

EXAMPLE 3

A reductant precursor in accordance with the invention,2-isopropoxy-1,4-anthraquinone (IPAQ), was prepared as hereinafterdescribed. 1.6 grams of 1,4-anthraquinone in 10 ml of acetic anhydridewas treated with 0.8 ml of borontrifluoride etherate. The1,4-anthraquinone went into solution slowly with a slight temperaturerise (to 40° C.) and after two hours, crystals of the triacetate beganto separate. After standing overnight at room temperature, thecrystalline product had separated from the dark brown solution. Thesolid was collected and washed with methanol. The material collected wascrystalline, weighing 1.34 grams without purification. The mixture wasstirred with 1.0 grams of sodium methoxide in 20 ml of methanol yieldingthe dark red sodium salt 2-hydroxy-1,4-anthraquinone. This salt wascollected and washed with methanol. Then it was dissolved in 100 ml ofH₂ O and the solution was filtered and acidified with hydrochloric acid.The 2-hydroxy-1,4-anthraquinone collected was a light yellow powder andthe yield was 0.75 grams.

4 grams of 2-hydroxy-1,4-anthraquinone synthesized as described above,20 ml of isopropanol and 12 ml of borontrifluoride etherate were heatedat 70° C. overnight, yielding the desired product,2-isopropoxy-1,4-anthraquinone. After cooling, the solution wasfiltered, dried, and washed with standard KHSO₄. Finally, the productwas washed with water and dried at room temperature overnight.

EXAMPLE 4

A reductant precursor in accordance with the invention,2,3-dichloro-1,4-anthraquinone, was prepared as hereinafter described. Amixture of α, α, α', α'-tetrabromo-o-xylene (4.22 grams), sodium iodide(10.0 grams), 2,3-dichloro-1,4benzoquinone (2.0 grams) and drydimethylformamide (35 ml) was stirred at 80°-90° C. for 24 hours. Afterpouring into cold water, the iodine color was discharged by the gradualaddition of aqueous sodium bisulfate. The brown precipitate was airdried overnight to yield 1.6 grams of crude2,3-dichloro-1,4-anthraquinone.

EXAMPLE 5

A reductant precursor in accordance with the invention,2,3-dichloro-6,7-diphenyl-1,4-naphthoquinone, was prepared ashereinafter described. 2,3-diphenylbutadiene (9 grams) and2,3-dichlorobenzoquinone (13.8 grams) and acetic acid (100 ml) werestirred at 75° C. for 20 hours. The resulting acetic acid solution wasdiluted and the precipitated product collected and dissolved inchloroform (100 ml). The solution was extracted with an aqueous solutionof 2 N NaOH. The light yellow colored organic layer was dried overmagnesium sulfate, filtered and evaporated to give the solid compound.

EXAMPLE 6

2-chloro-3-isopropoxy-1,4-anthraquinone, a reductant precursor inaccordance with the invention, was prepared from2,3-dichloro-1,4-naphthoquinone by a method similar to that described inExample 1.

EXAMPLE 7

2-chloro-3-isopropoxy-6,7-diphenyl-1,4-naphthoquinone, a reductantprecursor in accordance with the invention, was prepared from2,3-dichloro-6,7-diphenyl-1,4-naphthoquinone by a method similar to thatdescribed in Example 1.

EXAMPLES 8-22

Tellurium imaging films were made and tested, some utilizing reductantprecursors not in accordance with the present invention and other filmsutilizing the reductant precursors of the present invention. Theeffectiveness of the various reductant precursors was evaluated bymaking identical tellurium imaging films except for the type ofreductant precursor. Each film was made by combining the specificreductant precursor and amount as set forth in the following table with0.65 grams of bis(acetophenone) tellurium dichloride (a telluriumimaging compound), 0.625 grams of a masked 1-phenyl-3-pyrazolidone ofthe formula ##STR25## 2.4 grams of ortho-methoxy benzyl glyceryl ether(a diol), 10.42 grams of CAB-500-5 (matrix) containing an additional 1.5milliliters of water and 160 milliliters of a 50:50 mixture (by volume)of methylene dichloride and methyl ethyl ketone (solvent). Thecomponents were stirred together in complete darkness at roomtemperature until a homogeneous viscous solution was obtained. Thesolution was then coated on a MYLAR substrate at an area coverage ofapproximately 2 grams of bis(acetophenone) tellurium dichloride persquare meter. The resulting film was heated in an oven at 50°-55° C. forthree hours.

The photographic response of the film was evaluated by determining thewavelength of light at which maximum absorbtion took place and bydetermining the maximum wavelength of light to which the film wassensitive. The speed of the film was evaluated by determining the amountof energy required to produce an optical density of one greater thanfog. The minimum and maximum optical density of the film was determinedby exposing the film to imaging energy through a photographic steptablet having eleven steps and an optical density range of approximately0.5 to 3.05. The step tablet was in contact with the film duringexposure. A Honeywell Strobonar Model No. 710 Xenon flash tube wasutilized to provide imaging energy, spaced approximately 10 inches fromthe film. After exposure, the film was developed by heating the film ata temperature of 150°-155° C. for 40-45 seconds. The maximum opticaldensity (OD MAX) and minimum optical density or fog (OD MIN) wasdetermined with a MacBeth Model T-P 504 Densitomer using a red filter.

The films utilizing the various reductant precursors exhibited thefollowing results:

EXAMPLE 8

    ______________________________________                                        Reductant Precursor                                                                            Results                                                      ______________________________________                                         ##STR26##      Speed (@ OD of one over fog)  1,800 ergs/cm.sup.2 OD                          Min0.47 OD Max3.12 Spectral Sensitivity Maximum                               Sensitivity365 nm Upper Range Sensitivity412                  ______________________________________                                                        nm                                                        

EXAMPLE 9

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR27##      Speed (@ OD of one over fog) greater than 30,000                              ergs/cm.sup.2 OD Min0.55 OD Max2.79 Spectral Sensitivity                      Maximum Sensitivity @435 nm Upper Range Sensitivity550        ______________________________________                                                        nm                                                        

EXAMPLE 10

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR28##      Speed (@ OD of one over fog) greater than 30,000                              ergs/cm.sup.2 OD Min0.21 OD Max1.13 Spectral Sensitivity                      Maximum Sensitivity430 nm Upper Range Sensitivity560          ______________________________________                                                        nm                                                        

EXAMPLE 11

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR29##      Speed (@ OD of one over fog)  1,900 ergs/cm.sup.2 OD                          Min0.55 OD Max2.79 Spectral Sensitivity Maximum                               Sensitivity490 nm Upper Range Sensitivity550                  ______________________________________                                                        nm                                                        

EXAMPLE 12

    ______________________________________                                        Reductant Precursor                                                                        Results                                                          ______________________________________                                         ##STR30##                                                                                 Speed (@ OD of one over fog) greater than 30,000                              ergs/cm.sup.2 OD Min0.53 OD Max1.13 Spectral Sensitivity                      Maximum Sensitivity not determined Upper Range                                Sensitivity not determined                                       ______________________________________                                    

EXAMPLE 13

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR31##      Speed (@ OD of one over fog)  20,000 ergs/cm.sup.2 OD                         Min0.54 OD Max1.82 Spectral Sensitivity Maximum                               Sensitivity460 nm Upper Range Sensitivity510                  ______________________________________                                                        nm                                                        

EXAMPLE 14

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR32##      Speed (@ OD of one over fog)  16,000 ergs/cm.sup.2 OD                         Min0.51 OD Max1.95 Spectral Sensitivity Maximum                               Sensitivity470 nm Upper Range Sensitivity510                  ______________________________________                                                        nm                                                        

EXAMPLE 15

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR33##      Speed (@ OD of one over fog)  21,000 ergs/cm.sup.2 OD                         Min0.57 OD Max2.02 Spectral Sensitivity Maximum                               Sensitivity490 nm Upper Range Sensitivity510                  ______________________________________                                                        nm                                                        

EXAMPLE 16

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR34##      Speed (@ OD of one over fog)  4,900 ergs/cm.sup.2 OD                          Min0.46 OD Max2.05 Spectral Sensitivity Maximum                               Sensitivity470 nm Upper Range Sensitivity520                  ______________________________________                                                        nm                                                        

EXAMPLE 17

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR35##      Speed (@ OD of one over fog)  2,600 ergs/cm.sup.2 OD                          Min0.43 OD Max2.41 Spectral Sensitivity Maximum                               Sensitivity480 nm Upper Range Sensitivity610                  ______________________________________                                                        nm                                                        

EXAMPLE 18

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR36##      Speed (@ OD of one over fog)  8,200 ergs/cm.sup.2 OD                          Min0.47 OD Max1.83 Spectral Sensitivity Maximum                               Sensitivity510 nm Upper Range Sensitivity580                  ______________________________________                                                        nm                                                        

EXAMPLE 19

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR37##      Speed (@ OD of one over fog)  2,170 ergs/cm.sup.2 OD                          Min0.50 OD Max2.43 Spectral Sensitivity Maximum                               Sensitivity490 nm Upper Range Sensitivity550                  ______________________________________                                                        nm                                                        

EXAMPLE 20

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR38##      Speed (@ OD of one over fog)  2,330 ergs/cm.sup.2 OD                          Min0.47 OD Max2.31 Spectral Sensitivity Maximum                               Sensitivity490 nm Upper Range Sensitivity550                  ______________________________________                                                        nm                                                        

EXAMPLE 21

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR39##      Speed (@ OD of one over fog)  2,510 ergs/cm.sup.2 OD                          Min0.56 OD Max2.56 Spectral Sensitivity Maximum                               Sensitivity490 nm Upper Range Sensitivity550                  ______________________________________                                                        nm                                                        

EXAMPLE 22

    ______________________________________                                        Reductant Precursor                                                                           Results                                                       ______________________________________                                         ##STR40##      Speed (@ OD of one over fog)  1,460 ergs/cm.sup.2 OD                          Min0.47 OD Max2.60 Spectral Sensitivity Maximum                               Sensitivity510 nm Upper Range Sensitivity580                  ______________________________________                                                        nm                                                        

While the invention has been described with respect to preferredembodiments, it is to be understood that the invention is capable ofnumerous rearrangements, modifications and changes which will beapparent to one skilled in the art and it is intended that the inventionencompass such rearrangements, modifications and changes which fallwithin the scope of the appended claims.

We claim:
 1. A film for forming an image comprising a composition on asubstrate, which composition comprises:(a) an image forming telluriumcompound; (b) a reductant precursor which will abstract labile hydrogenfrom a labile hydrogen source under the influence of imaging energy tobecome a reducing agent with respect to the image forming telluriumcompound, said reductant precursor selected from the group consisting of3-chloro-2-isopropoxy-1,4-naphthoquinone,2-isopropoxy-1,4-anthraquinone, 3-chloro-2-isopropoxy-1,4-anthraquinone,3-chloro-2-(3'-pentoxy)-1,4-naphthoquinone,3-chloro-2-(2'-butoxy)-1,4-naphtoquinone,3-chloro-2-(3',3'-dimethyl-2'-butoxy)-1,4-naphtoquinone and2,3-diisopropoxy-1,4-naphthoquinone; (c) a source of labile hydrogen forreaction with said reductant precursor; and (d) a matrix in which saidtellurium compound, reductant precursor and source of labile hydrogenare combined in amounts effective which may be applied to a substrate 2.The film as recited in claim 1, wherein there is additionally provided adiol of the formula ##STR41## wherein each of R⁴ and R⁵ independentlyrepresents hydrogen, a hydrocarbon group, including straight chain,branched chain and cyclic hydrocarbon groups, hydroxyalkyl groups,alkoxycarbonyl groups, cycloalkyl groups or aryl groups; and Zrepresents a direct C-C bond between the carbon atoms on either side ofit, or an arylene group, the group (--C.tbd.C--), the group (--CR⁶═CR⁷)_(n), wherein n represents 1 or 2, and each of R¹² and R¹³represents hydrogen or an alkyl group or taken from part of acarbocyclic or heterocyclic ring, said diol being provided in an amountequivalent to at least 2 moles thereof per 1 mole of said telluriumforming compound.
 3. The film as recited in claim 1 wherein there isprovided a diol of the formula

    R.sup.7 --X--CH.sub.2 --CHOH--CH.sub.2 OH

wherein R⁷ is alkyl, alkanoyl, thiazolinyl, alkenyl, benzyl,alkylbenzyl, alkoxybenzyl, hydroxyalkylbenzyl, and halobenzyl; the alkylradical having from 1 to 7 carbon atoms; and X is oxygen or sulphur. 4.The film as recited in claim 1, wherein said tellurium compound isselected from the group consisting of ##STR42## in the foregoingformulae, R being an organic radical containing at least 1 carbonylgroup, R² being the residue of an ethylenic hydrocarbon, Hal beinghalogen, x being 1, 2 or 3; and x+y=4; n being an integer from 1 to 4and m+n=4.
 5. The film as recited in claim 3, said composition furthercomprising a masked reducing agent.
 6. The film as recited in claim 3wherein said composition further comprises an alcohol.
 7. The film asrecited in claim 1 wherein said composition further comprises water. 8.The film as recited in claim 5 wherein said composition furthercomprises a base.
 9. The film as recited in claim 1 wherein saidreductant precursor is 3-chloro-2-isopropoxy-1,4-naphthoquinone.
 10. Thefilm as recited in claim 1 wherein said reductant precursor is2-isopropoxy-1,4-anthraquinone.
 11. The film as recited in claim 1wherein said reductant precursor is3-chloro-2-isopropoxy-1,4-anthraquinone.
 12. The film as recited inclaim 1 wherein said reductant precursor is3-chloro-2-(3'-pentoxy)-1,4-naphthoquinone.
 13. The film as recited inclaim 1 wherein said reductant precursor is3-chloro-2-(2'-butoxy)-1,4-naphthoquinone.
 14. The film as recited inclaim 1 wherein said reductant precursor is3-chloro-2-(3',3'-dimethyl-2'-butoxy)-1,4-naphthoquinone.
 15. The filmas recited in claim 1 wherein said reductant precursor is2,3-diisopropoxy-1,4-naphthoquinone.
 16. A composition responsive toactivating energy for forming an imaging film, which compositioncomprises:(a) an image forming tellurium compound; (b) a reductantprecursor, which will abstract labile hydrogen from a labile hydrogensource under the influence of imaging energy to become a reducing agentwith respect to the image forming tellurium compound, said reductantprecursor selected from the group consisting of3-chloro-2-isopropoxy-1,4-naphthoquinone,2-isopropoxy-1,4-anthraquinone, 3-chloro-2-isopropoxy-1,4-anthraquinone,3-chloro-2-(3'-pentoxy)-1,4-naphthoquinone,3-chloro-2-(2'-butoxy)-1,4-naphthoquinone,3-chloro-2-(3',3'-dimethyl-2'-butoxy)-1,4-naphthoquinone and2,3-diisopropoxy-1,4-naphthoquinone; (c) a source of labile hydrogen forreaction with said reductant precursor; and (d) a matrix in which saidtellurium compound, reductant precursor and source of labile hydrogenare combined in amounts effective which may be applied to a substrate.17. The composition as recited in claim 16, wherein there isadditionally provided a diol of the formula ##STR43## wherein each of R⁴and R⁵ independently represents hydrogen, a hydrocarbon group, includingstraight chain, branched chain and cyclic hydrocarbon groups,hydroxyalkyl groups, alkoxycarbonyl groups, cycloalkyl groups or arylgroups; and Z represents a direct C--C bond between the carbon atoms oneither side of it, or an arylene group, the group (--C.tbd.C--), thegroup (--CR⁶ ═CR⁷)hd n, wherein n represents 1 or 2, and each of R¹² andR¹³ represents hydrogen or an alkyl group or taken from part of acarbocyclic or heterocyclic ring, said diol being provided in an amountequivalent to at least 2 moles thereof per 1 mole of said telluriumforming compound.
 18. The composition as recited in claim 16 whereinthere is provided a diol of the formula

    R.sup.7 --X--CH.sub.2 --CHOH--CH.sub.2 OH

wherein R⁷ is alkyl, alkanoyl, thiazolinyl, alkenyl, benzyl,alkylbenzyl, alkoxybenzyl, hydroxyalkylbenzyl, and halobenzyl; the alkylradical having from 1 to 7 carbon atoms; and X is oxygen or sulphur. 19.The composition as recited in claim 16, wherein said tellurium compoundis selected from the group consisting of ##STR44## in the foregoingformulae, R being an organic radical containing at least 1 carbonylgroup, R⁸ being the residue of an ethylenic hydrocarbon, Hal beinghalogen, x being 1, 2 or 3; and x+y=4; n being an integer from 1 to 4and m+n=4.
 20. The composition as recited in claim 16, said compositionfurther comprising a masked reducing agent.
 21. The composition asrecited in claim 18 wherein said composition further comprises analcohol.
 22. The composition as recited in claim 16 wherein saidcomposition further comprises water.
 23. The composition as recited inclaim 20 wherein said composition further comprises a base.
 24. A methodfor recording electromagnetic radiation, comprising imagewise impingingsaid radiation upon a photosensitive film to produce a change in atleast one property thereof, which film is a photosensitive compositioncarried by a substrate, which composition comprises:(a) an image formingtellurium compound; (b) a reductant precursor, which will abstractlabile hydrogen from a labile hydrogen source under the influence ofimaging energy to become a reducing agent with respect to the imageforming tellurium compound, said reductant precursor selected from thegroup consisting of 3-chloro-2-isopropoxy-1,4-naphthoquinone,2-isopropoxy-1,4-anthraquinone, 3-chloro-2-isopropoxy-1,4-anthraquinone,3-chloro-2-(3'-pentoxy)-1.4-naphthoquinone,3-chloro-2-(2'-butoxy)-1,4-naphthoquinone,3-chloro-2-(3',3'-dimethyl-2'-butoxy)1,4 -naphthoquinone and2,3-diisopropoxy-1,4-naphthoquinone; (c) a source of labile hydrogen forreaction with said reductant precursor; and (d) a matrix in which saidtellurium compound, reductant precursor and source of labile hydrogenare combined in amounts effective which may be applied to a substrate.25. The method as recited in claim 24, wherein there is additionallyprovided a diol of the formula ##STR45## wherein each of R₄ and R₅independently represents hydrogen, a hydrocarbon group, includingstraight chain, branched chain and cyclic hydrocarbon groups,hydroxyalkyl groups, alkoxycarbonyl groups, cycloalkyl groups or arylgroups; and Z represents a direct C--C bond between the carbon atoms oneither side of it, or an arylene group, the group (--C.tbd.C--), thegroup (--CR⁶ ═CR⁷)_(n), wherein n represents 1 or 2, and each of R¹² andR¹³ represents hydrogen or an alkyl group or taken from part of acarbocyclic or heterocyclic ring, said diol being provided in an amountequivalent to at least 2 moles thereof per 1 mole of said telluriumforming compound.
 26. The method as recited in claim 24 wherein there isprovided a diol of the formula

    R.sup.7 --X--CH.sub.2 --CHOH--CH.sub.2 OH

wherein R⁷ is alkyl, alkanoyl, thiazolinyl, alkenyl, benzyl,alkylbenzyl, alkoxybenzyl, hydroxyalkylbenzyl, and halobenzyl; the alkylradical having from 1 to 7 carbon atoms; and X is oxygen or sulphur. 27.The method as recited in claim 24, wherein said tellurium compound isselected from the group consisting of ##STR46## in the foregoingformulae, R being an organic radical containing at least 1 carbonylgroup, R⁸ being the residue of an ethylenic hydrocarbon, Hal beinghalogen, x being 1, 2 or 3; and x+y=4; n being an integer from 1 to 4and m+n=4.
 28. The method as recited in claim 24, wherein saidcomposition further comprises a masked reducing agent.
 29. The method asrecited in claim 26, wherein said composition further comprises analcohol.
 30. The method as recited in claim 24 wherein said compositionfurther comprises water.
 31. The method as recited in claim 28 whereinsaid composition further comprises a base.
 32. The method of claim 24wherein the tellurium compound is bis(acetophenone) telluriumdichloride.
 33. The composition recited in claim 16 wherein saidreductant precursor is 3-chloro-2-isopropoxy-1,4-naphthoquinone.
 34. Thecomposition of claim 16 wherein said reductant precursor comprises2-isopropoxy-1,4-anthraquinone.
 35. The composition of claim 16 whereinsaid reductant precursor comprises3-chloro-2-isopropxy-1,4-anthraquinone.
 36. The composition of claim 16wherein said reductant precursor comprises3-chloro-2-(3'-pentoxy-1,4-naphthoquinone.
 37. The composition of claim16 wherein said reductant precursor comprises3-chloro-2-(2'-butoxy)-1,4-naphthoquinone.
 38. The composition of claim16 wherein said reductant precursor comprises3-chloro-2-(3',3'-dimenthyl-2'-butoxy)-1,4-naphthoquinone.
 39. Thecomposition of claim 16 wherein said reductant precursor comprises2,3-diisopropoxy-1,4-naphthoquinone.